The iambic trimeter derives its name from its essential shape, which is three metrical units (hence trimeter) which are each basically iambic in form. The iambic metron has the following shape (where the x is an anceps, the - is a longum, and the u is a brevis):
Hence, reversing the current running though a wire will have the affect of reversing the direction of the magnetic force at a point some distance away from the wire. The affect that this has on the overall magnetic field depends on the shape of the wire.
Tesla believed that alternating current (or AC) was the solution to this problem. Alternating current reverses direction a certain number of times per second -- 60 in the U.S. -- and can be converted to different voltages relatively easily using a transformer.